Bleaching pulp



Jan. 9, 1940. H. L. JoAcHlM r 2,186,487

` LEAcHING`PuLP Filed sept. 22, 193e A TTORNEY Patented Jan. 9, 1940PATENT ori-lcs 2.156.491 v BLEACEING PULP Herman l.. Joachim. SanFrancisco. Calif., as-

Ilm

or to Maui Agricultural Co. Ltd., a corporation of the Territory ofHawaii f Application September 22. 1988, Serial No. 281,199

schim.

'Ihis invention relates to the chemical reilning and purification of abagasse pulp and to the production of a new alpha cellulose pulpcontaining 96% and more alpha cellulose, having a low soda solubility,low copper number, a negligible ether solubility and a materially higherreactivity as compared to the reactivity of cotton linters andsuper-refined wood pulps.

With a constantly increasing demand for alpha cellulose by the nlm,rayon, explosives and plastics industries, and .with the inherentlimitation on alpha cellulose pulps derived from wood. namely an alphacellulose 'content of 95% and less, a copper number of 0.8 to 1.0, asoda solubility of 3%f3.6% and an ether solubility of from 0.2%0.5%,attention has been given to the production of alpha cellulose from othercellulosic materials.

While bagasse is one of the most important u cellulose bearing crops,because sugar cane from which itis obtained can be rapidly grown,utilization oi' bagasse as an alpha cellulose source has heretofore notbeen economically practical. While the literature contains variousstatements u to the effect that bagasse pulp can be treated according tomethods suitable to wood pulp,- I have found that in fact this was notso. Presumably the diillculties in treating bagas'se pulp according tothe methods heretofore employed upon wood pulp have largely failedbecause of the complexity of the bagasse fiber bundles and because ofthe difference which characterizes bagasse from wood.

I have found that a bagasse pulp, after suitable delignicationoperation, such as that dis,v

closed in my copending application with John P. Foster, Serial No.164,212, filed September 16, 1937. can be suitably treated to produce apulp of high alpha cellulose content, low copper num- 40 her,satisfactory viscosity, low soda solubility,

and negligible ether solubility.

Ihave further found that when care is taken not to degrade the pulpduring refining and purification, a pulp is produced of high alphacellulose content, 96% and higher. And, further. what is even moreimportant, the pulp has such a physical fibrous structure that itadsorbs water and aqueous solutions, swells and reacts with thosereagents commonly employed in the acetate, nitrate, cuprammonium andviscose process far more rapidly and completely than do the alphacellulose materials known heretofore such as cot" ton linters andsuper-refined wood pulp.

Depending on the degree of delignification 4effected in the pulpingoperation, a bagasse pulp,

as produced from the sugar cane grown in the Hawailan Islands willrequire 31/2% to 5% by weight on a dry basis of total chlorine to removeimpurities present. I have found that initially the pulp, co while inaqueous suspension, should be subject to When it is desired to produce apulp containing only alpha cellulose, this treatment can be made moredrastic, and as much as '75% of the initial chlorine demand supplied inthe ilrst of a plurality oi' chlorinating stages. An excessive increasein the initial chlorine supplied degrades the pulp, lowering the yieldof alpha cellulose,

lowering the viscosity and increasing the copper number. While thevalues given are relatively critical for the particular bagasse, andwill be critical for other like bagasses, vsugar canes grown in otherlocalities differ and these percentages may accordingly vary. v

Afterthe initial chlorination operation, I have found that the pulpshould be separated from the initial chlorination liquor, washed andthen treated with a caustic solution.- Thereafter substantially all theremaining chlorine demand is supplied, preferably as a hypochloritebleach liquor. v

When an alpha cellulose pulp of high alpha content is desired,I 96% andhigher, the pulp is further treated with strong caustic solution, washedand treated with a mineral acid to adjust the viscosity of the pulp.Finally, the pulp is bleached with a very light hypochlorite bleach. Thenew 96% and higher alpha cellulose pulp of this invention isparticularly characterized' in having some properties'comparable tothose of a high grade of cotton linters. as will be apparent from aconsideration of the properties appearing in the following table.

Sli Cotton Bagasse Property re ned llntei'l pulp wood pulp Alphacellulose content....... 98% 00 98% 94 -95% Co pernumber ..0.15- 0.2502-0.22 0.8- 1.0 Sn ssolubility-...; 2 8.57 2 2.57 8.0- 3.26% Ethersolubility 0.15 0.a 0.05% 0.2- 0.a a

rials known heretofore), it can be stated that alpha cellulose contentof 86% and a copper number of 1.0. It was produced according to theprocess of the aforementioned copending application. v

The pulp was placed man aqueous suspension of 3-3.E consistency andchlorinated by the addition of 65% of its total chlorine demand. Thechlorination was permitted to continue until only a trace of chlorinecould be found. Usually from 20 to 30 minutes were required. During thechlorination the temperature was held at about room tempel ature, andwas .not permitted to exceed 80 F. It was found that if the temperatureexceeded 80 F. the pulp was degraded. It was also found that thechlorination could be carried on with from 62.5?/0--6'1570 of the totalchlorine demand if a high cellulose pulp, 96% and higher, was desiredfrom this bagasse pulp, although bagasse pulps from other types of canemay vary as to the initial chlorine supplied. The thing to avoid Wasover-chlorination. Some bagasse pulps, by reason of differences in theirinherent properties traceable to the original cane and the` l regionswherein it was grown, could stand more chlorine than others Withoutsacrificing quality and yield.

After the chlorination had continued until only a trace of chlorine wasleft, the pulp was washed. I have successfully employed a continuousvacuum viasher, utilizing Warm water and washing until the pH of theWash Water had risen to pH 6.5-6.8. Thereafter the pulp was diused withan alkaline water. The Water and pulp were heated to 12W-124 from 45 to60 minutes being required. The pulp, in the aqueous suspension, was heldat this temperature for about an hour. The consistency of the pulp inthis step was from 5% to 6%, while initially about 2/% of caustic sodaon the dry weight of the pulp was added. More or less caustic soda couldbe employed, but this, it was found, would serve only to decrease orincrease the time of treatment. After the diffusion treatment, the pulpwas again Washed on a vacuum Washer with warm water until the pH hadfallen to pH 8.2-8.6.

'I'he operations previously recited were carried on continuously or asbatch operations, vas desired.

The pulp was next treated with a hypochlorite solution, preferably asodium hypochlorite bleach, although calcium hypochlorite can beemployed. Substantially all the chlorine required to remove impuritieswas added here, and I preferably employed about 25% of the totalchlorine demand. The pH of the hypochlorite solution Was held initiallyon the acid side and within the limit of carbonio acid so that, ineffect, the operation was carried on with hypochlorous acid. 'I'he pulpconsistency was about 8%. but as high as 16% consistency could beemployed. To facilitate control this operation was usually handled as abatch operation.

the 96% or higher alpha cellulose pulp ci this' After the pulp had beensubjected to the action ofthe hypochlorlte for about minutes, causticsoda was added to alkalize the bleach liquor and solubilize anychlorination products. I! the caustic was not'v added, the final pulpwasnot as bright. I have successfully added a 1% caustic soda solution toalkalize the pulp suspension, although more or less could be used. Afterthe f addition of the caustic soda, about 45 minutes were permitted toelapse, after which the hypochlorite treated pulp was washed on a vacuumwasher with Warm water.

The pulp was then refined and to this end it kwas subjected to theaction oi a strong caustic solution. I preferably employed onecontaining from 1.4 to 1.8 parts of caustic for each part of pulp on adry basis. This refining treatment was continued for about 2 hours at anelevated temperature, preferably in the neighborhood of 204 F., orbetween 202 F. and 206" 1l'. 'This served to dissolve impurities presentand raise the alpha cellulose content to the neighborhood of 96%.

When 98% alpha cellulose was desired, the

strength of the caustic solution employed was increased toward 1.8 and Ihave successfully employed a ratio of 1 part of pulp to 1.75 parts ofcaustic; in producing the 96% cellulose a ratio of 1 part of pulp to1.64 parts of caustic was employed. The consistency of the pulp duringre- 5 lning could be varied, butI have successfully used about 4%consistency. At the end of the refining operation it was found that thecopper number had dropped to about 0.2. After the caustic treatment, thepulp was Washed until the pH of the Wash water had dropped to about9.5-10.

The refined pulp was treated to adjust its viscosity. This treatment wascarried on at about room temperature for 20 to 30 minutes, with asuitable concentration of a mineral acid such as hydrochloric acid, thepulp being at about 4% consistency. I have found the temperature duringthe acid treatment should not exceed 80 F. Above this temperature thepulp was ruined rapidly.

Depending on the desired viscosity of the pulp.,

more or less acid was employed. Other acids as sulphuric, nitric andphosphoric could be used. In one case I employed 7 liters of 36% HC1 to200 pounds of dry pulp. This served to give a pulp of a viscosity of 25to 38 centipoises in a 1% solution. The acid treated pulp was thenWashed on a continuous vacuum washer until the pH oi' the wash Water haddropped to about pH 7.2-7.6.

Because the treatment with a strong caustic tended to give a grayishcast, which the acid treatment removed almost but not entirely, Ipreferably concluded the purification with a'nal bleach with ahypochlorite solution. This bleach was almost instantaneous, removingwhatever gray cast was present in the pulp almost instantly. Theremaining chlorine required to make up the initial total chlorine demandwas added here as a hypochlorite, either sodium or calcium. The quantitywas usually 10% or less of that required initially. The temperature waskept below 80n F. and usually at about room temperature. The bleach wasusually very rapid, and 20 to 30 minutes usually sufllced. Thereafterthe pulp was Washed until the pH of the Wash water was about 7.4-7.8.The pulp was then ready for thickening and drying. The pulp producedaccording to this process was particularly characterized by its highalpha cellulose content,

with lower grades of alpha cellulose materials,

the initial chlorine supplied was increased, and I have used as much as75%. This chlorine was vleft in contact, with the pulp until only atrace remained when the pulp was washed. After washing, the pulp wassubjected to a caustic solution containing about 1 part oi pulp to 1.15parts caustic by weight. Holding the pulp in this solution andy treatingit for about 2 hours at 204 F. served to increase the alpha cellulosecontent of the resulting pulp to about 90%. A strongly alkaline solutioncould not be used in this renning operation because the highlychlorinated pulp was quite sensitive to it. Thereafter the material waswashed and. depending on the viscosity, was treated with a mineral acidas hydrochloric acid. The acid step was omitted when the viscosity wassatisfactory. Thereafter the final chlorineV demand was supplied, assodium hypochlorite, this operation being carried out below 80 F. andusually at about room temperature. The pulp wasflnally washed.

It is to be understood that conventional equipment can be employed incarrying on the i'oregoing procedures.

I claim:

1. A process for purification of a substantially delignified butsubstantially otherwise untreated bagasse pulp to produce a high gradealphacellulose pulp comprising treating an aqueous suspension o! saidpulp with free chlorine in an amount from about 62.5% to about 67.5% ofthe total chlorine demand of said pulp and at a temperature below about80 F., washing the chlorine treated pulp, treating the washed pulp withan alkaline liquor, washing the alkali treated pulp. treating .thewashed pulp with an acid hypochlorite solution containing substantiallyall additional chlorine required to oxidize remaining impurities.alkalizing said pulp during said hypochlorite bleach, washing thealkalized pulp, treating the pulp with a strong caustic solution, and

washing the pulp.

2. A process for purii'ication of a substantially delignified butsubstantially :otherwise untreated bagasse pulp to produce a high gradealphacellulose pulp comprising treating an aqueous suspension oi saidpulp with free chlorine in an amount from about 62.5% to about 67.5% ofthe total chlorine demand'of said pulp and a temperature below about 80F., washing the chlorine treated pulp, treating the washed pulp with analkaline liquor. washing the alkali treated pulp, treating the washedpulp witha hypochlorite solution containing substantially all additionalchlorine required to oxidize remaining impurities, alkalizing said pulpduring said hypochlorite bleach, washingk the alkalized pulp, treatingthe pulp further with a strong caustic solution containing !rom about1.4 to about 1.8 parts of caustic for each part of pulp on a dry basis.and washing the pulp.

3. A process for purification of a substantially lulose pulp comprisingtreating an aqueous suspension oi' said pulp with free chlorine in anamount from about 62.5% to about 67.5% of the total chlorine demand ofsaid pulp and at a temperature below` about 80 F., washing the chlorinetreated pulp, treating the washed pulp with an alkaline liquorcontaining about 21/2% caustic soda on the dry weight of the pulp and ata temperature of about 120 F. to render said pulp alkaline, washingthe-alkali treated pulp, treating the washedpurifled pulp with ahypochlorite solution containing substantially all additional chlorinerequired to oxidize remaining impurities, treating the hypochloritetreated pulp with an alkaline solution, washing the alkalized pulp,treating the pulp for about two hours at about 204 F. with a strongcaustic solution containing from about 1.4 to about 1.8 parts of causticfor each part oi pulp on a dry basis, and washing the pulp.

4. A-process for purication o1' a substantially delignified butsubstantially otherwise untreated bagasse pulp to produce. a high gradealpha-cellulose pulp comprising treating an aqueous suslpension of saidpulp with free chlorine in an deligniiied but substantially otherwiseuntreated bagassee pulp to produce a high grade alpha-celamount fromabout 62.5% to about 67.5% of the total chlorine demand of said pulp andat a temperature below about 80 F., washing the chlorine treated pulp.treating the washed pulp with an alkaline liquor, washing the alkalitreated pulp, treating the washed purified 'pulp with a hypochloritesolution containing substantially all additional chlorine required tooxidize remaining impurities, treating said pulp with an alkalinesolution to render said pulp alkaline, washing the alkalized pulp,treating the pulp with a strong caustic solution containing from about1.4 to about1.8 parts of caustic for each part of pulp on a dry basis,washing the pulp with a dilute acid' at a temperature below about 80 F.to acidity the pulp, and washing the pulp with water.

5. A process for purification of a substantially delignified butsubstantially otherwise untreated bagasse pulp to produce a high gradealpha-cellulose pulp comprising treating an aqueous suspension of saidlpulp with free chlorine in an amount from about 62.5% to about 67.5% ofthe total chlorine demand of vsaid pulp and at a temperature below about80 F., treating the pulp with an alkaline solution, washing the alkalitreated pulp. treating the washed pulp with a hypochlorous acid solutioncontaining substantially all additional chlorine required to oxidizeremaining impurities, treating the pulp with an alkaline solution torender the pulp alkaline. washing the alkalized pulp. treating the pulpfurther with a strong caustic solution. and washing the pulp.

'6. A process i'or purification of a substantially deligniiiedbut'substantially otherwise untreated bagasse pulp to produce a highgrade alpha-cellulose pulp comprising treating an aqueous suspension ofsaid pulp with free chlorine in an amount of from about 62.5% to about67.5% oi the total chlorine demand of said pulp and at a temperaturebelow about 80 F., washing the.

chlorine treated pulp, and thereafter treating the pulp alternately withcaustic solutions and acid chlorine solutions and washing the pulp aftereach treatment.

HERMAN L. JOACHIM.

